1765 Cooling our jets

Scrubbing the Sky: Inside the Race to Cool the Planet
by Paul McKendrick

Vancouver: Figure 1 Publishing, 2023
$28.95  / 9781773272085

Reviewed by Douw Steyn


The strange “naked ape” we are has been on planet earth as a distinct species for about 200,000 years. Most of that time we spent migrating across all continents, but Antarctica, and scratching out a survival as hunter gatherers. About 10,000 years ago we discovered how to subvert amenable plant and animal species so as to produce vast riches of food. This allowed us to settle in concentrated cities, develop our languages, art, literature and science, and much of what we today think of as our uniquely human heritage. About 200 years ago we discovered how to harness the energy stored in fossilized carboniferous deposits. This energy greatly accelerated the development of a diverse array of technologies that made our lives easier and more comfortable, and made possible an unprecedented and fast rise in human population.

However, the burning of these fossil fuels had an unintended consequence – the accumulation of carbon dioxide and methane in Earth’s atmosphere. This accumulation opened the previously closed carbon-oxygen cycle that is partly responsible for maintaining the relatively stable average global climate that has prevailed since the end of the last great glaciation some 12,000 years ago.

Consequences of the global climate disruption include an increase in average global temperature, a rise in mean sea-level and changes in ecological conditions that support much of Earth’s biodiversity. At 8 billion people, and the associated level of energy use, resource use and material consumption, we have reached a point of “ecological overshoot” at which we are using roughly 2.5 planet earths to support us.

Paul McKendrick. Photo by Eva Urbanska

While it is unlikely that a continuation of this developmental trajectory will cause our extinction, it is not unreasonable to expect that a possible future is one in which the conditions under which we live become so constricted that much of what we value becomes significantly diminished.

It is with this as a backdrop that a relatively new technology called Direct Air Capture (DAC) of atmospheric carbon dioxide has developed. This is the subject of Scrubbing the Air by Paul McKendrick.

Scrubbing the Air is thus one in a substantial line of books examining the people behind scientific discoveries and engineering developments. Prominent recent books in this category are: The making of the Atomic Bomb by Richard Rhodes, Longitude by Dave Sobel and Fermat’s Last Theorem by Simon Singh. Scrubbing the Air does not have the depth of new and terrible discovery documented by Rhodes. It does not chronicle an individual’s heroic struggle with technique and bureaucracy recounted by Sobel. It does not have any of the mystery, passion and persistent dedication written about by Singh.

Scrubbing the Air is nonetheless a thorough, if rather detailed chronicle of efforts since the mid 1990s to develop DAC into a viable technology that could strip carbon dioxide out of the free atmosphere in a way that is economically viable. The book is largely about the people behind the development of DAC, rather than the scientific and engineering underpinnings of DAC. The book is written primarily from the author’s perspectives deriving from his careers in the energy sector; financing renewable energy projects; the oil and gas sector; the electric utility sector and investment banking.

One of the major themes in Scrubbing the Air is that of technical innovation driven by competition. The first competition of interest being Richard Branson’s 2007 prize for a technology capable of removing one billion tonnes of carbon equivalent (amounting to 3.7 billion tonnes of carbon dioxide) per year from the atmosphere. The story of this prize is mirrored by the similar story of Elon Musk’s early 2020s XPRIZE for solutions to atmospheric carbon dioxide, though much more diffuse, and less ambitious that Branson’s prize. The Branson prize was not awarded, and the XPRIZE competition is still underway. These two competitions bookend nine short chapters, each describing a particular approach to DAC, and introducing the reader to the various entrepreneurs, engineers and venture capitalists active in each approach.

Image from Scrubbing the Sky. Courtesy Figure 1 Publishing

The book’s dust jacket does not identify an intended audience, but a reading leads to the impression that the intended audience appears to be the technically inclined lay person with an interest in entrepreneurship and investment. Strangely, however, McKendrick never makes any judgements about the overall viability of DAC as a means to achieve meaningful reduction of atmospheric carbon dioxide. This is a disappointment as the book clearly is based on considerable research of the subject matter. In one sense, the book is a disappointment precisely because it does not lead readers to a reasoned take-away message. Many people who have heard of DAC will be wondering if the technique and the related industry offer solutions to the climate crisis we face. Scrubbing the Air does not offer any judgements on the question. That many of the founders, engineers and scientists quoted in the book express clear and strong opinions on the question makes it all the more surprising that McKendrick does not venture an opinion.

I have two major criticisms of Scrubbing the Air. It takes a largely USA-centric approach to the development and prospects of DAC. At the worst, the book refers to financial and/or taxation measures specific to the USA. The most glaring example is to be found on Page 113, which refers, without explanation, to: “the 45Q tax credit and California Low-Carbon Fuel Standard.” Global warming is a global problem, and carbon capture must be exercised on a global scale. No mention is made of DAC efforts in the EU, China or India.

The closing chapter, titled “The Prize”, is in some ways the most interesting. Here, one of the quoted interviewees talks of the DAC machine called “MechanicalTree” (at Arizona State University). MechanicalTree is capable of removing 40 tonne of carbon dioxide per year from the atmosphere. If there were 1 billion MechanicalTrees (equal to the number of cars on earth today), it would take 37.5 years to capture 1.5 trillion tonnes of CO2 – reducing atmospheric CO2 by 100 parts per million (ppm). This equates to approximately the amount of carbon dioxide humans have emitted into the atmosphere since the industrial revolution. One billion machines means there would have to be an installation roughly every one km of land surface. The target performance in Musk’s competition is a removal rate of 1000 tonnes per year. If such a device were available, we would need 5 million of them (spaced every 10 km) to achieve a 100 ppm reduction in 30 years. These simple calculations reveal the real difficulty of DAC.

Barely mentioned in Scrubbing the Air will be the need to find non-carbon energy sources to power the DAC devices. Similarly, bare mention is made of the requirement that captured carbon (in whatever chemical form) will have to be stored in a depository that will not allow subsequent release of carbon (as carbon dioxide) to the atmosphere. These and related questions are left unattended, and leave the reader wondering where all this leads to.

“So long as there is a market for carbon dioxide” is the closing sentence of the book. This statement neatly captures the overall approach of Scrubbing the Air, which is to achieve DAC through investment, commercialization and startups. By any logic, the reduction of atmospheric carbon dioxide to combat climate change is an imperative to restore the atmospheric global “commons” It has been repeatedly demonstrated that growth-motivated and profit-driven utilitarian markets are notoriously incapable of delivering “common” goods. Restoring the atmospheric commons is therefore unlikely to be achieved by the approaches that dominate consideration in Scrubbing the Air. A book on DAC that has the lay public as an audience must consider at least private-public partnerships, if not global government approaches to carbon capture.


Douw Steyn

Douw Steyn is an Emeritus Professor of Earth, Ocean and Atmospheric Sciences at UBC. He was educated at the University of Cape Town (Physics & Applied Mathematics) (B.Sc hons., 1967, M.Sc. 1968) and the University of British Columbia (Ph.D, 1980). He is active in the fields of air pollution meteorology, boundary layer meteorology, mesoscale meteorology, environmental science, and interdisciplinary science. He is an authority on ozone pollution in the Lower Fraser Valley and applied meteorology in complex terrain. He describes himself as “Physicist by training, atmospheric scientist by vocation, environmentalist by inclination.”


The British Columbia Review

Publisher and Editor: Richard Mackie

Formerly The Ormsby Review, The British Columbia Review is an on-line book review and journal service for BC writers and readers. The Advisory Board consists of Jean Barman, Wade Davis, Robin Fisher, Barry Gough, Hugh Johnston, Kathy Mezei, Patricia Roy, Maria Tippett, and Graeme Wynn. Provincial Government Patron (since September 2018): Creative BC. Honorary Patron: Yosef Wosk. Scholarly Patron: SFU Graduate Liberal Studies.

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